Numerous fuel fired appliances have an igniter for igniting the fuel upon command. Fuel fired appliances include, for example, heating, ventilation, and air conditioning (HVAC) appliances such as furnaces, boilers, water heaters, as well as other HVAC appliances. Non-HVAC fuel fired appliances include, for example, clothes dryers, washing machines, stoves, ovens, as well as others.
Fuel fired appliances typically have a combustion chamber and a burner. A fuel source, such as a gas or oil, is typically provided to the burner through a valve or the like. In many cases, various electrical and/or electromechanical components are provided to help control and/or otherwise carry out the intended function of the fuel fired appliance. For example, various controllers, motors, igniters, blowers, switches, motorized valves, motorized dampers, and/or others, are often included in, or are used to support, a fuel fired appliance. Typically, these electrical and/or electromechanical components receive power from an electrical power source, such as a line voltage supply (e.g. 120 volt 60 Hz AC). The line voltage supply is often used to power higher power electrical and/or electromechanical components of the fuel fired appliance, such as blowers, igniters, etc., if any. In some cases, a transformer is provided to step down the incoming line voltage supply to a lower voltage supply that is useful in powering lower voltage electrical and/or electromechanical components if present, such as controllers, motorized valves or dampers, thermostats, etc. The lower voltage supply can be, for example, a 24 volt 60 Hz AC voltage.
In one example, a fuel-fired appliance may include an electronic ignition system, such as a hot surface igniter, for initiating burner ignition of the fuel-fired appliance. When activated, the hot surface igniter is typically configured to ignite gas in the burner of the fuel-fired appliance, without the need for a pilot light. Such electric ignition systems can often reduce gas consumption and increase the efficiency of the fuel-fired appliance.
There are several different types of hot surface igniters available for use in fuel-fired appliances. A few examples include silicon nitride igniters, silicon carbide igniters, and mini silicon carbide igniters. Hot surface igniters may be constructed from a variety of materials including, for example, aluminum nitride, silicon nitride, silicon carbide, boron carbide, tungsten disilicide, tungsten carbide, and/or mixtures thereof.
In some cases, hot surface igniters can provide some advantages over other types of igniters. However, due to the operating characteristics of the materials used in many of these igniters, as well as the extreme variations in temperature experienced by these igniters, proper control of the input power that is ultimately delivered to the hot surface igniter is often desirable to achieve optimum results. Providing too little power to the hot surface igniter can prevent the fuel-fired appliance from igniting because the hot surface igniter will not become hot enough. Providing too much power to the hot surface igniter can, in some cases, cause it to get too hot and prematurely burn out. As such, proper control of the power supply for the hot surface igniter can be desirable to achieve increased performance and a longer life for the hot surface igniter.
A hot surface igniter is often powered by a higher voltage supply, such as a line voltage supply, in order to achieve the desired temperature in a desired time period. The control of the activation and deactivation of the hot surface igniter is often controlled by a controller that is powered by a lower voltage supply, such as a microprocessor or the like. In some cases, a voltage difference may develop or be present between the ground reference of the line voltage supply and the ground reference of the lower voltage supply. This ground reference difference can cause control problems, particularly when, for example, a controller powered by a lower voltage supply is attempting to control an electrical component (such as a hot surface igniter) that is driven by a line voltage supply.